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LibJS: Make mapped arguments objects way less allocation-happy
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Browse source 
By following the spec to the letter, our mapped arguments objects ended
up with many extra GC allocations:

- 1 extra Object for the internal [[ParameterMap]].
- 2 extra NativeFunctions for each mapped parameter accessor.
- 1 extra Accessor to hold the aforementioned NativeFunctions.

This patch removes all those allocations and lets ArgumentsObject model
the desired behavior in custom C++ instead of using script primitives.

1.06x speedup on Speedometer's TodoMVC-jQuery.
This commit is contained in:
Andreas Kling 2025-05-11 12:32:24 +02:00 • committed by Andreas Kling
commit a0864dbb26
Notes: github-actions[bot] 2025-05-11 12:01:34 +00:00
3 changed files with 63 additions and 44 deletions
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14
Libraries/LibJS/Runtime/ArgumentsObject.h
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2021, Andreas Kling <andreas@ladybird.org>
* Copyright (c) 2021-2025, Andreas Kling <andreas@ladybird.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -20,24 +20,26 @@ public:
virtual void initialize(Realm&) override;
virtual ~ArgumentsObject() override = default;
Environment& environment() { return m_environment; }
virtual ThrowCompletionOr<Optional<PropertyDescriptor>> internal_get_own_property(PropertyKey const&) const override;
virtual ThrowCompletionOr<bool> internal_define_own_property(PropertyKey const&, PropertyDescriptor const&, Optional<PropertyDescriptor>* precomputed_get_own_property = nullptr) override;
virtual ThrowCompletionOr<Value> internal_get(PropertyKey const&, Value receiver, CacheablePropertyMetadata*, PropertyLookupPhase) const override;
virtual ThrowCompletionOr<bool> internal_set(PropertyKey const&, Value value, Value receiver, CacheablePropertyMetadata*, PropertyLookupPhase) override;
virtual ThrowCompletionOr<bool> internal_delete(PropertyKey const&) override;
// [[ParameterMap]]
Object& parameter_map() { return *m_parameter_map; }
void set_mapped_names(Vector<FlyString> mapped_names) { m_mapped_names = move(mapped_names); }
private:
ArgumentsObject(Realm&, Environment&);
[[nodiscard]] bool parameter_map_has(PropertyKey const&) const;
[[nodiscard]] Value get_from_parameter_map(PropertyKey const&) const;
void set_in_parameter_map(PropertyKey const&, Value);
void delete_from_parameter_map(PropertyKey const&);
virtual void visit_edges(Cell::Visitor&) override;
GC::Ref<Environment> m_environment;
GC::Ptr<Object> m_parameter_map;
Vector<FlyString> m_mapped_names;
};
}